Historically, copper tubes have been the industry norm for HVAC manifolds. Aluminum tubing has been gaining acceptance in recent years. However, there are additional challenges in closing the ends of aluminum tubes. Tube ends can be closed via a spin tube operation that is known in the art. The spin tube operation closes the tube end, but then braze is applied to strengthen the tube end and make it leak-proof and burst-proof. With copper tubes, when braze material is applied to the closed tube end, the viscosity of the brazing medium would form a raised area, resulting in an adequate thickness and strength of the brazed tube end.
With aluminum tubes, however, this prior art method is insufficient. That is because the low viscosity of the aluminum braze alloy causes the alloy to flow over the sides of the tube, instead of thickening on the end of the tube as desired. TIG welding can be used to strengthen the aluminum tube ends, but TIG welding requires specialized welders, safety features and shielding that make it more expensive and time consuming. Brazing is easier than TIG welding and requires no eye protection and no shielding.
The method of the present disclosure solves the problem of closing the end of aluminum tubes by indenting the tube ends after they are spun closed to form a concave tube end. The concave tube end is then brazed, and the braze alloy collects in the concavity and forms a sufficient thickness to strengthen the tube end adequately.
For purposes of summarizing the invention, certain aspects, advantages, and novel features of the invention have been described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any one particular embodiment of the invention. Thus, the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.